For the production of a polypeptide such as a recombinant protein, methods for introducing a nucleic acid encoding the polypeptide into prokaryotes, yeast, insect cells, protozoa, mammalian cells, or the like by using a plasmid vector or a virus vector, and transcribing and translating the nucleic acid by using a protein production system in the host cell are used. Especially, a method using mammalian cells is suitable for studies or clinical applications in the fields of not only protein engineering and molecular genetics but also immunoengineering, gene therapy, and pharmaceutical product production because the post-translational modification is the same as that of human and a protein derived from a mammal can be correctly folded, etc.
However, in the method for producing a recombinant protein using a mammalian cell, the product is often insufficiently obtained compared with the methods using prokaryotes or yeast. As techniques for solving this problem, for example, the technique in which an episomal maintenance system and a strong promoter/enhancer are added to a protein expression system having a transactivation system in a recombinant protein expression system using a human cell (Patent Literature 1), and the technique for improving an expression of a protein under the control of an expression regulatory region having CMV promoter and trans-activation-responsive region (hereinafter, referred to as TAR) by a binding action of human TRBP that is a binding factor of TAR of human immunodeficiency virus type 1 (hereinafter, referred to as HIV-1) to TAR (Non-Patent Literature 1) are known.